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AA6005A-T6 aluminum hollow extrusions were friction stir welded at a fixed high welding speed of 2000 mm/min and various rotation speeds. The results showed that the heat-affected zone (HAZ) retained the similar grain structure as the base material except some grain coarsening, and the density of dislocations and β′ precipitates were almost unchanged, indicating that the high welding speed inhibited the coarsening and dissolution of β″ precipitates via fast cooling rate. The thermo-mechanically affected zone (TMAZ) was characterized by elongated and rotated grains, in which a low density of β′ precipitates and the highest density of dislocations were observed. The highest heat input and severest plastic deformation occurring in the nugget zone (NZ) resulted in the occurrence of dynamic recrystallization and a high density of dislocations. Hence, all the β″ precipitates and most of the β′ precipitates dissolved into the matrix, and a few β′ precipitates were transformed into β precipitates. The microhardness was controlled by the precipitation and solution strengthening in the HAZ, by the dislocation and precipitation strengthening in the TMAZ, and by the fine-grain and dislocation strengthening in the NZ. With the increase in rotation speed, the peak and the lowest microhardness value increased monotonously.

Cu-15Ni-8Sn alloy is a spinodal hardened alloy which possesses excellent combination of strength, elastic modulus, corrosion resistance and wear resistance. Much concern focuses on the microstructures and properties of this wrought alloys after heat treatment, however, the microstructure feature of the alloy during hot plastic deformation processing is rarely declared. The microstructure evolution of the hot-extruded Cu-15Ni-8Sn alloy with different extrusion ratio were investigated by optical microscope, scanning electronic microscope, electron backscattered diffraction. The results showed that dynamic recrystallization occured during hot extrusion at extrusion ratio ranging from 6 to 17. With the increase of extrusion ratio, the fraction of recrystallized grain increased. However, the amount of discontinuous γ precipitates reduced. The cellular structure was observed to grow not only on grain boundaries but also in the coarsening annealing grains when the extrusion ratio was below 13. When extrusion ratio was 17, the discontinuous γ precipitates and the residual annealing grains were suppressed and some recrystallized grains grew up.